It is a common practice in the art to recover cottonseed from the lint which remains after the cotton product itself is separated from the crop. The seeds so recovered are used for the production of cottonseed oil and for planting purposes.
One of the methods commonly employed for the removal of lint from cottonseed is the hydrogen chloride gas method known as the anhydrous hydrogen chloride gas method. This method involves injecting HCl gas into a closed reaction chamber which contains a charge of fuzzy seed. The HCl gas reacts with the lint on the seed and the seed is then emptied from the reaction chamber into a buffer. In the buffer, the lint is buffed from the seed by means of rotating screens.
A typical prior art apparatus for carrying out the hydrochloric gas method is shown in the schematic block diagrams of FIGS. 1 and 2. In the prior art apparatus shown in FIG. 1, hydrogen chloride is stored under pressure in liquid form and taken off under pressure in gaseous form from an HCl trailer 10, which is positioned outside the building in which the delinting process is carried out, through copper tubing 12 until the gas reaches the building and then through pipes 20 within the building itself. The pipes 20 are typically what is known in the art as "Schedule 40 black pipe", which is a steel pipe having a "Schedule 40" thickness. The HCl is stored in the trailer 10 under a pressure in the range of about 500 to 700 pounds per square inch (psi) and typically is in liquid form as stored, with a portion of the storage volume not occupied by the liquid being occupied by HCl in gaseous form. The HCl may thus be taken off either in liquid or gaseous form but is taken off in gaseous form in the typical prior art system.
As the HCl gas is removed from the trailer 10, it is carried through the copper tubing 12 and then through the pipes 20 through an electrically actuated ball valve 14 to a heat exchanger 18. The HCl gas is expanded through the electrically actuated ball valve 14 and then introduced into the heat exchanger 18 and, in the process of this first expansion, the temperature is reduced to the range of about -200.degree. F. before the gas enters the heat exchanger. The heat exchanger 18 typically uses heated oil as the heat exchange medium. The HCl gas is circulated through heat exchange coils within the heat exchanger. The temperature of the oil in the heat exchanger 18 is typically maintained at about 150.degree. F. with the purpose of warming the HCl gas to above the water freezing temperature of 32.degree. F.
After the HCl gas passes through the heat exchanger 18, it is carried through Schedule 40 black pipe 20 through a regulating check valve 16 and a flow meter 22 and into a revolving delinting drum 24. The flow meter 22 is typically an orifice type element which produces a pressure drop proportional to the flow rate of the HCl gas through the orifice. This pressure drop is sensed and is used to control the regulating check valve 16 to regulate the flow rate of the HCl gas at a selected level through the system.
Thus, as the tubes of HCl in the HCl trailer are individually accessed, the pressure in each tube is reduced as the gas is withdrawn from the tube and the flow meter 22 indicates the manual adjustments needed for the regulating check valve 16 to maintain the desired flow rate. The desired flow rate is thus maintained until the full charge of HCl gas is delivered for treating a batch of fuzzy seed in the revolving delinting drum 24. After the fuzzy seed is treated with the HCl gas in the revolving drum 24, the seed is removed for further processing as will now be explained.
The delivery and processing of the fuzzy seed is shown in the flow chart of FIG. 2. The fuzzy seed to be delinted is initially stored in a hopper feeder 26 and is delivered, typically by an auger (not shown), through an elevator 28 into a dryer drum 30. The seed is preheated in the dryer drum 30 to about 140.degree. F. After removal from the dryer drum 30, the fuzzy seed is conveyed by an elevator 32 to a charge cart where the seed is weighed out in the proper batch size, typically in a batch size of about 2,000 to 2,500 pounds.
The charge cart 34 is typically a wheeled vehicle powered by an electric drive which, after measurement of the proper batch amount, injects the seed into the revolving delinting drum 24 bypassing a boot pit 36 in the process. The HCl gas for treating the fuzzy seed injected into the revolving delinting drum 24 is introduced by means of the gas flow control system of FIG. 1. During the treatment of the seed with HCl gas the temperature of the delinting drum 24 itself is maintained at a constant temperature of about 145.degree. F. by an external heater (not shown). The 145.degree. F. temperature level also serves to eliminate any pink boll worm and other infestations which may be present in the fuzzy seed.
After the fuzzy seed is treated with the HCl gas in the delinting drum 24, the drum 24 is tilted at an angle and the seed is dumped into the boot pit 36 from where it is conveyed by an elevator 38 to buffing reels 40 and then by an elevator 42 to a clipper cleaner 44. The buffing reels 40 remove by mechanical action the fibers which have been weakened by the HCl treatment and the clipper cleaner 44 removes foreign material, small seeds and cracked seed particles.
In prior art HCl systems of the type shown in FIGS. 1 and 2, the typical amount of HCl gas used to treat the fuzzy seed is in the range of about 12 to 13.6 pounds of HCl gas per ton of fuzzy seed depending upon the variety of the seed, the moisture content of the seed, the amount of lint on the seed and other such factors. Some portions of the seed treated in such prior art systems typically exhibit damage which has been thought to be heat damage due perhaps to overheating of some of the HCL gas or to hot spots within the drum during treatment. It was also suspected that such overheating may have affected the overall yields of the system in terms of gas use per ton of seed treated.
In addition, in such prior art systems it was found that when the delinting drum 24 is opened for removal of the seed after treatment of the seed with HCl gas, some HCl gas is released indicating that gas remains which has not reacted with the seed. HCl gas which escapes from the system combines with moisture in the atmosphere to form hydrochloric acid. The escaping HCl gas is thus not only requires that workers operating the system wear protective equipment but is also causes corrosion of the plant equipment and creates maintenance problems.
In addition, in such prior art systems, the pH of the seed as it is removed from the delinting drum (after a processing time in the drum of about 10 to 12 minutes) is about 2.8 and anhydrous ammonia (NH.sub.3) is therefore used to neutralize the seed and the lint, thereby adding to the cost of treating the seed. After treatment with NH.sub.3, the pH of the seed is about 4.0 to 4.2 and the pH of the lint is about 2.2. In such prior art systems, about 7.8 to 9.0 pounds of NH.sub.3 is used per ton of seed processed.
Further, leakage problems have been encountered in such prior art systems. Because of the problem of leakage of HCl gas from the prior art systems, such systems have been operated only in arid climates in order to avoid the combination of the HCl gas with water to form hydrochloric acid and the resultant hazards and corrosion problems which would result. Nevertheless, because of the leakage of HCl gas which does occur, serious corrosion problems causing frequent maintenance of the equipment have been encountered with such prior art systems even in arid climates.
In addition, when maintenance is required, the system must usually be opened and, in that process, some residual HCl gas which is present in the system is unavoidably released, thus causing further leakage and problems similar to those encountered when the drum 24 is opened after a run.